As woodburning stoves have become more prevalent, their effects on air pollution have increased. Clean air statutes directed at woodburning stoves have been enacted in a number of areas. Consumers are more aware of the problems associated with burning wood. Typical woodburning stoves emit relatively large amounts of smoke and particulates into the atmosphere and significant creosote deposits can build up on stove pipes and chimneys.
In an effort to make a cleaner burning stove, manufacturers have produced stoves employing various techniques such as secondary combustion chambers and catalytic converters. In addition to stoves specifically designed to be cleaner burning, retrofit units for existing stoves have been introduced to reduce the levels of smoke and cresote. Generally, the operation of known retrofit units is unpredictable at best, depending upon the base appliance on which it is installed. This marginal situation is the result of the retrofit converter being located too far from the wood stove firebox, causing the exhaust gases entering the catalyst of such a retrofit device to be at temperatures too low for optimum catalyst performance especially at lower heat outputs. Furthermore, known retrofit appliances do not provide for a preheat of the combustion gases exiting the woodburning stove before encountering the catalyst. During low heat output operation with known systems, the gases exiting the stove body are often at too low a temperature for sustained catalytic ignition. In such a situation, the catalytic converter can have little if any effect on the levels of undesirable effluents.
It is an object of this invention, therefore, to provide an exterior retrofit system for substantially improving combustion efficiency in solid fuel heating appliances.
Another object of the invention is a retrofit system which substantially reduces smoke output and cresote deposits.
A further object of the invention is an exterior retrofit system which is self-contained and requires no permanent or complicated modifications to the solid fuel heating apparatus.
Yet another object of the invention is a retrofit system which reduces emissions over a wide range of heat outputs and specifically at low heat output levels.
A still further object of this invention is a retrofit unit employing a catalyst having a replacement cost of one half to one third the cost of the catalyst of known catalytic devices.